aragonite
{{Short description|Calcium carbonate mineral}}
{{Infobox mineral
| name = Aragonite
| boxwidth =
| boxbgcolor = Orange
| image = Aragonite crystal - Los Molinillos, Ceunca, Spain - 4x3.6x3.5cm 100g.jpg
| imagesize =
| alt =
| caption = Aragonite from Los Molinillos, Cuenca, Spain, sample width about 4 cm
| category = Carbonate minerals
| IMAsymbol = Arg (not to be confused with arginine){{cite journal |last=Warr|first=L. N. |date=2021 |title=IMA–CNMNC approved mineral symbols |journal=Mineralogical Magazine |volume=85 |issue=3 |pages=291–320 |doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}
| molweight =
| strunz =
| dana =
| system = Orthorhombic
| class =
| symmetry =
| unit cell = l a = 4.9598(5) Å, b = 7.9641(9) Å, and c = 5.7379(6) Å at 25 °C{{cite journal | pmid=34876711 | year=1971 | last1=Dickens | first1=B. | last2=Bowen | first2=J. S. | title=Refinement of the Crystal Structure of the Aragonite Phase of CaCO(3) | journal=Journal of Research of the National Bureau of Standards Section A | volume=75A | issue=1 | pages=27–32 | doi=10.6028/jres.075A.004 | pmc=6715969 }}
| color = Can come in a variety of colors, but commonly red or white
| colour =
| habit = Commonly dendritic or pseudo-hexagonal; can also be acicular, tabular, prismatic, coral-like
| twinning = Cyclic on {110}, forms pseudohexagonal aggregates. If polysynthetic, forms fine striations parallel to [110].
| cleavage = Good on [110], Poor on {110}.
| fracture = Subconchoidal
| tenacity = Very brittle
| mohs = 3.5–4
| luster = Vitreous, waxy, resinous
| streak = White
| diaphaneity = Transparent to opaque
| gravity = 2.94
| density =
| polish =
| opticalprop = Biaxial (−)
| refractive = nω = 1.550 nε = 1.650
| birefringence = δ = 0.155
| pleochroism =
| 2V = Measured 18–19°
| dispersion = Weak
| extinction = Parallel
| length fast/slow =
| fluorescence = Faint white-blue to blue-violet
| absorption =
| melt =
| fusibility =
| diagnostic =
| solubility = Soluble in acids, and saltwater (but takes longer)
| impurities = Commonly strontium, zirconium, lead
| alteration =
| other = Thermodynamically unstable, Morphs slowly back into calcite
| prop1 =
| prop1text =
| references = {{cite web | url=https://geologyscience.com/minerals/aragonite | title=Aragonite Properties, Occurrence » Geology Science | date=26 October 2021 }}{{Mindat |id=307 |name=Aragonite}}}}
Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate ({{chem2|CaCO3}}), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
File:AragoniteFromCrystalMaker.png
The crystal lattice of aragonite differs from that of calcite, resulting in a different crystal shape, an orthorhombic crystal system with acicular crystal.{{cite journal |last=Bragg|first=William Lawrence |date=1924-01-01 |title=The structure of aragonite |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=105 |issue=729 |pages=16–39 |doi=10.1098/rspa.1924.0002 |bibcode=1924RSPSA.105...16B |issn=0950-1207|doi-access=free }} Repeated twinning results in pseudo-hexagonal forms. Aragonite may be columnar or fibrous, occasionally in branching helictitic forms called flos-ferri ("flowers of iron") from their association with the ores at the Carinthian iron mines.{{cite book |last1=Sinkankas |first1=John |title=Mineralogy for amateurs. |date=1964 |publisher=Van Nostrand |location=Princeton, N.J. |isbn=0442276249 |pages=371–372}}
Occurrence
The type location for aragonite is Molina de Aragón in the Province of Guadalajara in Castilla-La Mancha, Spain, for which it was named in 1797.{{cite book |title=Understanding Minerals & Crystals |publisher=Struik Nature |last1=Cairncross |first1=B. |last2=McCarthy |first2=T. |year=2015 |location=Cape Town |page=187 |isbn=978-1-43170-084-4}} Aragonite is found in this locality as cyclic twins inside gypsum and marls of the Keuper facies of the Triassic.{{Cite book |title=Minerales y Minas de España. Vol. V. Carbonatos y Nitratos |last=Calvo |first=Miguel |publisher=Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo |year=2012 |isbn=978-84-95063-98-4 |location=Madrid |pages=314–398}} This type of aragonite deposit is very common in Spain, and there are also some in France.
An aragonite cave, the Ochtinská Aragonite Cave, is situated in Slovakia.{{cite journal |last1=Pukanská |first1=Katarína |last2=Bartoš |first2=Karol |last3=Bella |first3=Pavel |last4=Gašinec |first4=Juraj |last5=Blistan |first5=Peter |last6=Kovanič |first6=Ľudovít |title=Surveying and High-Resolution Topography of the Ochtiná Aragonite Cave Based on TLS and Digital Photogrammetry |journal=Applied Sciences |date=4 July 2020 |volume=10 |issue=13 |pages=4633 |doi=10.3390/app10134633|doi-access=free }}
In the US, aragonite in the form of stalactites and "cave flowers" (anthodite) is known from Carlsbad Caverns and other caves.{{Cite book | author1-last=Gonzalez | author1-first=Luis A. |author2-last=Lohmann |author2-first=Kyger C. |chapter=Controls on Mineralogy and Composition of Spelean Carbonates: Carlsbad Caverns, New Mexico |editor1-last=James |editor1-first=Noel P. |editor2-last=Choquette |editor2-first=Philip W. |title=Paleokarst |pages=81–101 |publisher=Springer-Verlag |location=New York |date=1988 |isbn=978-1-4612-3748-8 |doi=10.1007/978-1-4612-3748-8}} For a few years in the early 1900s, aragonite was mined at Aragonite, Utah (now a ghost town).{{cite book |title=An Explorer's Guide: Utah |publisher=The Countryman Press |author=Balaz, Christine |year=2009 |location=Vermont |page=368 |isbn=978-0-88150-738-6}}
Massive deposits of oolitic aragonite sand are found on the seabed in the Bahamas.{{Cite journal |last1=Newell |first1=Norman D. |last2=Purdy |first2=Edward G. |last3=Imbrie |first3=John |date=1960 |title=Bahamian Oölitic Sand |journal=The Journal of Geology |volume=68 |issue=5 |pages=481–497 |doi=10.1086/626683 |bibcode=1960JG.....68..481N |s2cid=129571671 |issn=0022-1376}}
File:P-T Diagram for CaCO3.svg
Aragonite is the high pressure polymorph of calcium carbonate. As such, it occurs in high pressure metamorphic rocks such as those formed at subduction zones.{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=336–337}}
Aragonite forms naturally in almost all mollusk shells, and as the calcareous endoskeleton of warm- and cold-water corals (Scleractinia). Several serpulids have aragonitic tubes.{{cite book |last1=Boggs |first1=Sam |title=Principles of sedimentology and stratigraphy |date=2006 |publisher=Pearson Prentice Hall |location=Upper Saddle River, N.J. |isbn=0131547283 |edition=4th |pages=161–164}} Because the mineral deposition in mollusk shells is strongly biologically controlled,{{cite journal |last1=Belcher |first1=A. M. |last2=Wu |first2=X. H. |last3=Christensen |first3=R. J. |last4=Hansma |first4=P. K. |last5=Stucky |first5=G. D. |last6=Morse |first6=D. E. |title=Control of crystal phase switching and orientation by soluble mollusc-shell proteins |journal=Nature |date=May 1996 |volume=381 |issue=6577 |pages=56–58 |doi=10.1038/381056a0|bibcode=1996Natur.381...56B |s2cid=4285912 }} some crystal forms are distinctively different from those of inorganic aragonite.{{cite journal |last1=Chateigner |first1=D. |last2=Ouhenia |first2=S. |last3=Krauss |first3=C. |last4=Belkhir |first4=M. |last5=Morales |first5=M. |title=Structural distortion of biogenic aragonite in strongly textured mollusc shell layers |journal=Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms |date=February 2010 |volume=268 |issue=3–4 |pages=341–345 |doi=10.1016/j.nimb.2009.07.007|bibcode=2010NIMPB.268..341C }} In some mollusks, the entire shell is aragonite;{{cite journal |last1=Loftus |first1=Emma |last2=Rogers |first2=Keith |last3=Lee-Thorp |first3=Julia |author-link3=Julia Lee-Thorp |date=November 2015 |title=A simple method to establish calcite:aragonite ratios in archaeological mollusc shells: CALCITE:ARAGONITE IN ARCHAEOLOGICAL SHELLS |journal=Journal of Quaternary Science |volume=30 |issue=8 |pages=731–735 |doi=10.1002/jqs.2819 |s2cid=130591343}} in others, aragonite forms only discrete parts of a bimineralic shell (aragonite plus calcite). The nacreous layer of the aragonite fossil shells of some extinct ammonites forms an iridescent material called ammolite.{{cite journal |last1=Mychaluk |first1=Keith A. |last2=Levinson |first2=Alfred A. |last3=Hall |first3=Russel L. |title=Ammolite: Iridescent fossilized ammonite from southern Alberta, Canada |journal=Gems & Gemology |date=Spring 2001 |volume=37 |issue=1 |pages=4–25 |doi=10.5741/GEMS.37.1.4 |url=https://www.gia.edu/doc/Iridescent-Fossilized-Ammonite-from-Southern-Alberta-Canada.pdf |access-date=1 August 2021}}
Aragonite also forms naturally in the endocarp of Celtis occidentalis.{{Cite journal |author1=Wang, Jang |author2=Jahren, A. Hope |author3=Amundsen, Ronald |year=1996 |title=Potential For [Carbon 14] Dating Of Biogenic Carbon In Hackberry (Celtis) Endocarps |url=http://eoas.fsu.edu/sites/default/files/u12/Faculty-Misc/Wang/pubs/potential-Cdating-biogenic-carbonate-hackberry-endocarps.pdf |journal=Quaternary Research |volume=47 |pages=337–343 |doi=10.1006/qres.1997.1894 |s2cid=49232599}}{{Dead link|date=November 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
The skeleton of some calcareous sponges is made of aragonite.{{cite book |author1=Hooper, J. N. A. |url={{google books |plainurl=y |id=OQoxzqjQXWEC|page=220}} |title=Systema Porifera: A Guide to the Classification of Sponges |author2=Van Soest, R. W. M. |author3=Debrenne, F. |publisher=Kluwer Academic/Plenum |year=2002 |isbn=978-0-306-47260-2 |editor1=Hooper, J. N. A. |location=New York |pages=9–14 |contribution=Phylum Porifera Grant, 1836 |editor2=Van Soest, R. W. M.}}{{cite book |last=Bergquist |first=P.R. |title=Encyclopedia of Life Sciences |publisher=John Wiley & Sons |year=2001 |isbn=978-0-470-01617-6 |contribution=Porifera (Sponges) |doi=10.1038/npg.els.0001582}}
Aragonite also forms in the ocean inorganic precipitates called marine cements (in the sediment) or as free crystals (in the water column).{{cite journal |last1=Bialik |first1=Or M. |last2=Sisma-Ventura |first2=Guy |last3=Vogt-Vincent |first3=Noam |last4=Silverman |first4=Jacob |last5=Katz |first5=Timor |title=Role of oceanic abiotic carbonate precipitation in future atmospheric CO2 regulation |journal=Scientific Reports |date=24 September 2022 |volume=12 |issue=1 |pages=15970 |doi=10.1038/s41598-022-20446-7|pmid=36153366 |pmc=9509385 }}{{cite book |last1=Tucker |first1=Maurice E. |title=Carbonate sedimentology |date=1990 |publisher=Blackwell Scientific Publications |location=Oxford [England] |isbn=9781444314175}}
Inorganic precipitation of aragonite in caves can occur in the form of speleothems.{{sfn|Nesse|2000|p=337}} Aragonite is common in serpentinites where magnesium-rich pore solutions apparently inhibit calcite growth and promote aragonite precipitation.{{cite journal |last1=Bonatti |first1=E. |last2=Lawrence |first2=J.R. |last3=Hamlyn |first3=P.R. |last4=Breger |first4=D. |title=Aragonite from deep sea ultramafic rocks |journal=Geochimica et Cosmochimica Acta |date=August 1980 |volume=44 |issue=8 |pages=1207–1214 |doi=10.1016/0016-7037(80)90074-5|bibcode=1980GeCoA..44.1207B }}
Aragonite is metastable at the low pressures near the Earth's surface and is thus commonly replaced by calcite in fossils. Aragonite older than the Carboniferous is essentially unknown.{{Cite journal| doi = 10.1080/03115518508618971| title = Shell microstructures of Cambrian molluscs replicated by phosphate| year = 1987| last1 = Runnegar | first1 = B.| journal = Alcheringa: An Australasian Journal of Palaeontology| volume = 9| issue = 4| pages = 245–257 }}
Aragonite can be synthesized by adding a calcium chloride solution to a sodium carbonate solution at temperatures above {{convert|60|C}} or in water-ethanol mixtures at ambient temperatures.Sand, K.K., Rodriguez-Blanco, J.D., Makovicky, E., Benning, L.G. and Stipp, S. (2012) Crystallization of CaCO3 in water-ethanol mixtures: spherulitic growth, polymorph stabilization and morphology change. Crystal Growth & Design, 12, 842–853. {{doi|10.1021/cg2012342}}.
Physical properties
Aragonite is a thermodynamically unstable phase of calcium carbonate at any pressure below about {{convert|3000|bar||sp=us}} at any temperature.{{cite journal|last1=Carlson |first1=W.D. |year=1980 |title=The calcite–aragonite equilibrium: effects of Sr substitution and anion orientational disorder |journal=American Mineralogist |volume=65 |number=11–12 |pages=1252–1262 |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/65/11-12/1252/104707/The-calcite-aragonite-equilibrium-effects-of-Sr |access-date=31 July 2021}} Aragonite nonetheless frequently forms in near-surface environments at ambient temperatures. The weak Van der Waals forces inside aragonite give an important contribution to both the crystallographic and elastic properties of this mineral.{{Cite journal |last1=Ulian |first1=Gianfranco |last2=Valdrè |first2=Giovanni |date=2022-09-01 |title=Structural and elastic behaviour of aragonite at high-pressure: A contribution from first-principle simulations |url=https://www.sciencedirect.com/science/article/pii/S0927025622003457 |journal=Computational Materials Science |language=en |volume=212 |pages=111600 |doi=10.1016/j.commatsci.2022.111600 |hdl=11585/893023 |s2cid=250059382 |issn=0927-0256|hdl-access=free }} The difference in stability between aragonite and calcite, as measured by the Gibbs free energy of formation, is small, and effects of grain size and impurities can be important. The formation of aragonite at temperatures and pressures where calcite should be the stable polymorph may be an example of Ostwald's step rule, where a less stable phase is the first to form.{{cite journal |last1=Fyfe |first1=W.S. |year=1964 |title=Calcite aragonite problem |journal=AAPG Bulletin |volume=48 |number=4 |pages=526 |url=https://archives.datapages.com/data/bulletns/1961-64/images/pg/00480004/0500/05260.pdf |access-date=31 July 2021}} The presence of magnesium ions may inhibit calcite formation in favor of aragonite.{{cite journal |last1=Kitano |first1=Yasushi |last2=Park |first2=Kilho |last3=Hood |first3=Donald W. |title=Pure aragonite synthesis |journal=Journal of Geophysical Research |date=November 1962 |volume=67 |issue=12 |pages=4873–4874 |doi=10.1029/JZ067i012p04873|bibcode=1962JGR....67.4873K }} Once formed, aragonite tends to alter to calcite on scales of 107 to 108 years.{{cite book |last1=Blatt |first1=Harvey |last2=Middleton |first2=Gerard |last3=Murray |first3=Raymond |title=Origin of sedimentary rocks |date=1980 |publisher=Prentice-Hall |location=Englewood Cliffs, N.J. |isbn=0136427103 |edition=2d}}
The mineral vaterite, also known as μ-CaCO3, is another phase of calcium carbonate that is metastable at ambient conditions typical of Earth's surface, and decomposes even more readily than aragonite.{{cite journal | title=Differentiation of Calcium Carbonate Polymorphs by Surface Analysis Techniques – An XPS and TOF-SIMS study | last1=Ni | first1=M. | last2=Ratner | first2=B.D. | journal=Surf. Interface Anal. | year=2008 | volume=40 | issue=10 | pages=1356–1361 | doi=10.1002/sia.2904 | pmid=25031482| pmc=4096336 }}{{cite journal |last1=Kamiya |first1=Kanichi |last2=Sakka |first2=Sumio |last3=Terada |first3=Katsuyuki |title=Aragonite formation through precipitation of calcium carbonate monohydrate |journal=Materials Research Bulletin |date=November 1977 |volume=12 |issue=11 |pages=1095–1102 |doi=10.1016/0025-5408(77)90038-1}}
Uses
In aquaria, aragonite is considered essential for the replication of reef conditions. Aragonite provides the materials necessary for much sea life and also keeps the pH of the water close to its natural level, to prevent the dissolution of biogenic calcium carbonate.Orr, J. C., et al. (2005)
Anthropogenic ocean acidification over the 21st century and its impact on calcifying organisms. Nature 437: 681–686
Aragonite has been successfully tested for the removal of pollutants like zinc, cobalt and lead from contaminated wastewaters.Köhler, S., Cubillas, et al. (2007) Removal of cadmium from wastewaters by aragonite shells and the influence of other divalent cations. Environmental Science and Technology, 41, 112–118. {{doi|10.1021/es060756j}}
Gallery
Aragonite 2 Enguidanos.jpg|Aragonite crystals from Cuenca, Castile-La Mancha, Spain
Aragonite - Pantoja, Toledo, Castile-La Mancha, Spain.jpg|Aragonite crystal cluster from Spain
Image:BaculitesSuturesAragonite.jpg|Remnant biogenic aragonite (thin, rainbow-colored shell) on the ammonite Baculites (Pierre Shale, Late Cretaceous, South Dakota)
Aragonite layers in a blue mussel shell.jpg|Scanning electron microscope image of aragonite layers in the nacre of a blue mussel (Mytilus edulis)
Aragonit_-_Fluorescence.gif|Fluorescence of aragonite
See also
- Aragonite sea
- Ikaite, CaCO3·6H2O
- List of minerals
- Monohydrocalcite, CaCO3·H2O
- Nacre, otherwise known as "Mother-of-Pearl"
References
{{Reflist}}
External links
- [http://www.ssj.sk/en/jaskyna/12-ochtinska-aragonite-cave The Ochtinska Aragonite Cave in Slovakia]
- [https://web.archive.org/web/20090326063813/http://www.kosovocaves.com/ Kosovo Caves Aragonite Formations]
{{Authority control}}
Category:Orthorhombic minerals